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Subchapter 15. Petroleum Safety Orders--Refining, Transportation and Handling
Article 18. Unfired Pressure Vessels, Boilers, and Fired Pressure Vessels and Pressure Relief Valves
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§6858. Pressure-Relieving Devices.

(a) All pressure vessels shall be protected by a pressure relief device. Such relief devices shall be set to prevent the pressure in the vessel from exceeding limits established by the ASME Code or, where permitted, the Unfired Pressure Vessel Safety Orders. Pressure vessels that are connected together in a system with piping not containing valves that can isolate any pressure vessel while connected to its source or pressure may be considered as one unit.

(b) A vessel having a stop valve that can isolate the vessel from its pressure-relieving device, as permitted in subsection (c), shall be protected by an additional safety device, if the vessel may become entirely filled with liquid, and if it is possible that pressure may be generated by continued input of heat through exchanger tubes or similar devices or by exposure to sun or adjacent hot equipment. This additional safety device shall be connected to the vessel at all times except as permitted in subsection (c)(3). The additional safety device may be set at a pressure not greater than one and one-quarter times the maximum allowable working pressure.

(c) Stop Valves Between Pressure-Relieving Device and Vessel.

(1) A vessel in which pressure can be generated because of service conditions shall have no stop valve between the vessel and its pressure-relieving device except for inspection or repair purposes, as permitted in subsection (c)(3), or except in cases where multiple pressure-relieving devices are provided and the stop valves are so constructed that they can not be operated so as to reduce the pressure-relieving capacity below that required.

(2) A vessel in which the pressure originates from an outside source exclusively may have its pressure-relieving device on the vessel or at any point on the system between the vessel and its source of pressure, provided that the pressure-relieving device is set to function at not over the maximum allowable working pressure of the vessel. Under these conditions there may be a stop valve between the vessel and the pressure-relieving device which need not be locked open if the stop valve also closes the vessel from its source of pressure. Any stop valve between the pressure-relieving device and the vessel which does not close the vessel from its source of pressure shall meet the requirements given in subsection (c)(1) above.

(3) Stop valves may be installed between a pressure relief device and the operating vessel for the purposes of inspection, repair and/or replacement of the pressure relief device. Where stop valves are installed, the employer shall develop, implement, and maintain a written plan containing all of the following:

(A) Procedures to ensure that stop valves are open and locked or sealed during normal operations and are not to be closed except by a qualified person(s).

NOTE: In the case of multiple relief device installations having spare capacity or spare relief valves, the stop valve can be closed on the inactive relief valves providing sufficient system relief capacity is maintained.

(B) Procedures to minimize the frequency of closing stop valves while the vessel is in service. Stop valves shall remain open and locked or sealed until a replacement pressure relief device is available for installation.

Exception: Stop valves may be closed for emergencies such as pressure relief device failure.

(C) Procedures to ensure that a replacement pressure relieving device or needed replacement parts are readily available prior to closing the stop valve and removing the pressure relief device. An index for the location of all stop valves subject to this section shall be maintained.

(D) Before the removal of a pressure relief device from operating equipment, facility management shall review and approve a written operations plan for closing the stop valves. The plan shall incorporate, at a minimum, the following elements:

1. An engineering review to ensure that no increase in the capacity, pressure, severity, and/or operating condition of the unit or vessel will affect the safety of employees or equipment while the pressure relief device is out of service;

2. Provisions for written notification and operational procedures to unit controllers, operators and other affected personnel, including the safeguards and estimated time the valve will be out of service;

3. Identification of the functional position(s) or employees having knowledge of the operating equipment and pressure-relieving device(s) authorized to approve closing a stop valve; and,

4. Identification of the qualified person(s) or functional position(s) authorized to actually close and then reopen a stop valve.

(E) A written overpressure relief plan for each safety relief device shall be developed prior to closing the stop valve. The plan shall include:

1. The means by which overpressure-relief protection will be provided during the time that the pressure relief device is out of service;

2. The procedures to be followed to minimize the time that the stop valve will be closed;

3. The operating conditions, limitations, and other safety measures which are required to be observed to protect employees and equipment; and,

4. In the event that the plan requires a standby person to manually operate a vent to the atmosphere, a replacement safety relief valve shall be available for installation prior to closing the valve. Employees shall be protected from hazards as identified by Article 10 of the General Industry Safety Orders.

(F) The written overpressure-relief plan shall be made available to the Division upon request during the course of the work operation to which it applies.

(4) Valves as permitted above shall not be gate valves installed with the stems pointing above the horizontal plane of the valve body or globe valves installed so that the disk will open against pressure. This limitation need not apply to stop valves closing the vessel from its source of pressure. Other provisions acceptable to the Division may be used to assure that the valve is in the open position.

(d) Capacity of Pressure-Relieving Devices.

(1) The aggregate capacity of the pressure relief devices applied to any pressure vessel or system shall be sufficient to carry off the maximum quantity of material that can be generated in, or supplied to, the attached equipment without permitting a rise in pressure within the vessel above the limits permitted by the ASME Code.

(2) Pressure relief devices designed to relieve hydrostatic pressure caused by heat as outlined under subsection (b) shall have sufficient relieving capacity to prevent a hydrostatic pressure within the vessel in excess of 1.33 times the maximum allowable working pressure.

(e) Discharge lines from pressure relief devices shall be secured against movement. The lines shall be designed to facilitate drainage or shall be fitted with drains to prevent liquid entrapment in the discharge side of the relief device. The lines shall discharge at a location or in a manner to prevent injury to employees. The size of the discharge lines shall be such that any pressure that may exist or develop will not reduce the relieving capacity of the relief device below that required to properly protect the vessel. No valve shall be placed in a discharge line from a pressure relief device except when such discharge line discharges to a common header, in which case such valve shall be installed in compliance with subsection (c)(4) and locked or sealed open. Such valves may be closed only as allowed by subsection (c)(3).

(f) The employer shall maintain each pressure relief device installed on operating equipment so as to ensure the proper functioning of the device at the intended pressure. Such maintenance shall include inspection, testing, and the repair of the pressure relief device at frequencies as required by the service conditions.

(g) Pressure relief valve settings shall be changed only by authorized employees assigned such duties.

(h) A permanent and progressive record for each pressure vessel shall be maintained at the plant or the field office where the vessel is located. The record shall be available for inspection by the Division and shall include the following:

(1) The serial or identification number of the vessel.

(2) The established maximum allowable working pressure of the vessel.

(3) The coincident design temperature(s),

(4) Manufacturer's data reports, when obtainable, and any calculations used in establishing the maximum allowable working pressure.

(5) Such documents as necessary to record the results of tests, inspections, repairs, or alterations. Information on maintenance activities and events affecting the pressure vessel's integrity shall be included.

(i) Each pressure relief device in service shall have a serial or identification number stamped upon it and, in addition, a metal plate or tag shall be attached showing the pressure setting and the date the device was installed in service. A permanent and progressive record showing the serial or identification number, the location, the pressure setting, the date of installation in service, and the date of testing shall be maintained at the plant or field office where the pressure relieving device is located or at the supervising office.

Note: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.


1. New section filed 6-26-2006; operative 7-26-2006 (Register 2006, No. 26).

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